The present invention relates to an improved rubber-metal bushing and, more particularly, to an improved farruled rubber-metal bushing intended for use in the automotive structures. The present invention also relates to a method of producing such a bushing.
A typical rubber-metal bushing used in automobile suspensions to reduce or control vibration, ride, handling and noise comprises a central, inner metal tube which is surrounded by an elastomeric member. Both the tube and the member have a generally cylindrical geometry. The elastomer may be natural rubber or other selected elastomer having a selected durometer.
In use, a bolt is run through the inner metal tube and through adjacent structural or suspension members of an automobile frame. A nut is run onto the free end of the bolt and the mendsera are interconnected via the bushing by tensioning the bolt shaft between its head and the nut. The ends of the bushing, particularly the end surfaces of the elastomeric member, may bear against the structural/suspension members and/or the head of the bolt or the nut.
In the past where increased bearing surface or wearability of the bushing was required, ferrules were included in the bushing. These ferrules have comprised metallic cylindrical bodies and an integral annular flange. The cylindrical body of the ferrule is inserted into the inner metal tube of the bushing, with the flange overlying a selected amount of the end surface of the elastomeric member. The flange provides the increased bearing surface and wearability.
Where ferrules have been used as described above, they have typically been press-fit into the inner metal tube. Press fitting has been used to insure that the ferrules remain in place during shipment to their end users and when employed in automobile suspensions by automatic feeding equipment. To ensure that the ferrule-inner metal tube press-fit retained its integrity, the inner metal tube has usually been fabricated from seamless tubing which has been drawn over a mandrel ("DOM" tubing). Seamed tubes formed from flat stock ( which are standard in bushings not including ferrules) have until now been deemed unsuitable for bushings with press-fit ferrules. Such unsuitability has been thought to derive from the tendency of the seam of such tubing to open up following ferrules being press-fit thereinto. This quality of seamed tubing is often referred to as lack of "hoop strength".
The cost of high hoop strength DOM tubing is about two to three times that of formed tubes having seams. The initial acquisition cost of DOM tubing is higher than that of flat stock, and DOM tubing must be first cut to length and then finished on special equipment.
An object of the present invention is the formation of reliable rubber-metal bushings using seamed tubes and press-fit ferrules.